1. Field of the Invention
The present invention relates to casing hanger systems and other systems in which a tubular member is landed atop another. The invention also relates more broadly to devices and methods to relieve the problems generally related to stacked tubular members that are placed under high axial load conditions.
2. Description of the Related Art
In many conventional subsea wellheads, the upper end of the casing hanger engages a running tool by a seating arrangement wherein the casing hanger presents an annular upwardly and inwardly directed seating surface. One standard casing hanger top surface is a flat surface, angled at 15 degrees from the horizontal, facing upward and radially inward. The slope is intended to allow xe2x80x9ctrash,xe2x80x9d such as bits of rock and mud impurities, to fall off the top surface. The slope also aids in radially guiding and landing the running tool atop the casing hanger or in placing a second casing hanger atop a lower casing hanger. The running tool that engages the upper end of the casing hanger provides a complimentary downwardly and outwardly-directed annular engagement face. Sometimes, locking dogs are also used to aid in securing the two members together.
Unfortunately, this form of engagement has been found to be disadvantageous. The running tool exerts great weight loads onto the seating surface. Also, multiple casing hangers are often stacked upon one another. This is done when multiple casings are run. The additional casing hangers would also load the seating surface. The loads imparted to the casing hanger are directly related to the weight of the casing string sections being carried by the casing hanger and running tool. The loads are extremely high and may be in excess of a million pounds. The axial force applied to the upper end of the casing hanger by the running tool is damaging to the casing hanger and, as a result the upper end of the casing hanger may deflect radially outwardly reducing the engagement of the running tool and casing hanger. Radial deflection at the upper end of the casing hanger reduces the fatigue life of the casing hanger equipment.
A stacking arrangement for wellhead tubular members is described wherein the adjoining ends of the tubular members are specially shaped to prevent or limit outward radial deflection and the damage associated therewith. In an exemplary described embodiment, a casing hanger is provided with an upper longitudinal end having an inwardly sloped inner bearing surface and an inwardly sloped outer bearing surface. An outwardly sloped engagement surface adjoins the two bearing surfaces and is designed to be captured radially within a complimentary shaped surface on a running tool or other engaging member landed atop the casing hanger. A grooved section is provided to assist removal of trash from the upper end of the casing hanger.